Guanine nucleotide-binding proteins are involved in many pathways including signal transduction mediated by hormones, drugs and neurotransmitters (heterotrimeric "G" proteins) and in the regulation of cell growth and proliferation (approximately 21 kDa ras and ras-like proteins). ADP- ribosylation factors (ARFS) are approximately 20 kDa guanine nucleotide-binding proteins that were isolated based on their ability to enhance the enzymatic activity of cholera toxin. The physiological function(s) of ARF proteins is unknown. Injection of mRNA and protein into Xenopus oocytes has been used to investigate metabolic regulation and protein structure-function relationships. It has been shown that injection of ras p2l into Xenopus oocytes induces maturation whereas injection of monoclonal antibody against ras p2l prevents insulin- but not progesterone-induced maturation. To determine whether ARF might have functional effects like those of ras p2l, we examined the effects of microinjected ARF on progesterone- and insulin-stimulated maturation of Xenopus oocytes. In contrast to the findings with ras, maturation was inhibited by injection of ARF 3 to 8 h before exposure of oocytes to progesterone or insulin. ARF inhibition was dependent on progesterone concentration but not on insulin concentration. Inhibition was enhanced by concomitant injection of GTP and to a greater extent guanosine 5'-O-(3-thiotriphosphate)(GTPgammaS) which, in the absence of ARF, inhibited somewhat at early time points. The demonstration of this effect of ARF on both progesterone- and insulin-stimulated oocyte maturation may provide a clue to its physiologic role(s).